richah@aluxe.UUCP (ahrens) (11/20/84)
Yes, the present price for the Cushcraft R3, in my opinion,
is a bit steep, but it works. I purchased an R3 at Dayton in spring
of '83, $215 including shipping from Edge, Inc.
I did not install the antenna until Oct 1983. For background
information, Cushcraft announced the antenna in 1980. The R3 was
reviewed in the April '83 issue of CQ, pages 40 through 43. The
R3 is essentially an end fed 10, 15, & 20 meter trap half-wave vertical.
The matching network at the feed end consists of a tapped inductor
(the ring) in parallel with an air spaced variable capacitor driven
by a small motor. In my unit the drive motor is a 1 RPM Airpax (K81352-
P3-S2). The motor also drives a 1000 ohm pot for the simple control
box readout. The capacitor has 13 rotor plates and 14 stators, with
a rotor to stator spacing of .070". This is not the original
capacitor pictured in some of the early advertisement literature.
The number on my capacitor is 73175 27DEBB.
The antenna has a slim wind profile, and I mounted the R3 on
my chimney with an all stainless steel South River Model 2002
Chimney Mount (about $20). My XYL thinks it looks fine.
Ok now the shortcomings. After about one month, and a few rain
storms the tuning became erratic. I took the antenna down and
found water between the rotor and stator plates. I think the water
wicked down the threads of the ceramic feed-through screw, then down
the aluminum strap connecting the feed-through and the tuning capacitor.
The the water settled between the capacitor plates. The feed-through, the
cracks and seams in the plastic cover, the screw holes and the threads
should be sealed with RTV, I used Dow 3145 RTV Adhesive/Sealant. A
more severe design problem, in my opinion, is the use of aluminum
capacitor plates and threaded brass tie rods and nuts. In one month
their was evidence of corrosion or galvanic action between the brass
and aluminum. I replaced the aluminum strap connecting the feed-through
and capacitor with a homemade strap made of brass. I also replaced the
nickel plated feed-through screw with a brass screw and used brass nuts
on the feed-through. I covered the outside connection of the feed-through
with a good covering of RTV. The one end of the aluminum inductor
ring attaches to the feed-through. Also replace or RTV the screws on
the control cable terminal strip, they are steel.
Since Nov. '83 the antenna has performed quite well, I have worked
my share of DX during contests. The antenna presents a clean appearance
and DOES NOT REQUIRE RADIALS. I have been thinking about making a ground
mounted 40 meter version.
One other comment, I have an all electric home with a fire place
in the basement. I have not been using the fireplace for a few years.
If you should chimney mount a unit on an in-use chimney you
might have to mount the R3 higher to avoid the hot gases.
Best of luck and 73...................Rich Ahrens, W3WJC